The present invention relates to electrical connectors for printed circuit boards and more particularly, to what is commonly known as low or zero insertion force type connectors for making electrical contact with the electrical circuitry on printed circuit boards and the like.
It is desirable that printed circuit board connectors have high engagement and removal forces. This in turn results in high mating forces of the contacts with the conductive pads on the board. In some instances, this is by design such as when high pressure contacts are used to overcome bad surfaces (unwanted film or oxides) on the contact pads of the board, or in order to standarize connectors to accommodate large variations in printed circuit board thickness. A drawback inherent with high pressure contacts, however, is the difficulty in inserting and removing the board. To alleviate the problems of high mating forces which interfere with insertion and removal of the printed circuit boards, various types of zero force connectors have been designed.
Typical low or zero force type connectors for printed circuit boards comprise a housing assembly with a slot or opening therein to receive an edge portion of the printed circuit board and provided with contacts in the slot biased resiliently to cooperate with complimentary electrical terminal pads on the printed circuit board. These connectors generally fall into one of two types: (i) those in which the contacts are forced against the board after insertion of the board, and (ii) those in which the contacts are forced away from the board for insertion of the board, then allowed to spring back into contact with the pads on the board. In either type, the contacts are maintained out of the way temporarily to avoid interference with insertion of the printed circuit board, and to avoid damage and/or frictional wear on the contacts of the printed circuit board.
Various types of actuating devices have been designed for moving the contacts into and out of an engaging position with the printed circuit board to allow for easy insertion and/or removal of the printed circuit board from the connector. See for example U.S. Pat. Nos. 3,883,207; 3,638,167; 3,744,005; 3,636,499; 3,553,630; and 3,568,134.
However, low or zero insertion force type connectors to date have all provided a single actuating member for moving a plurality of contacts into or out of engagement, generally a single actuator member being provided for each side of the printed circuit board or substrate inserted into the connector. For example, in U.S. Pat. No. 3,475,717 entitled "Zero Force Connector," two series of contact members are provided on opposite sides of the slot into which the printed circuit board is received and are normally biased away from engagement to permit easy insertion of the printed circuit board without physical engagement with the contact members. After the circuit board is inserted into the slot of the connector, a pair of actuator plates, one for each series of contact members, are moved into impinging engagement with its series of resilient contact members to displace the contact members into engagement with the electrical circuitry on the circuit board.
In some instances, a single actuator member has been provided for actuating the contact members on both sides of the circuit board. For example, in U.S. Pat. No. 3,665,370, entitled "Zero Insertion Force Connector," a single actuator member serves to cam the series of contacts on either side of the printed circuit board into an engaging contact position upon rotation of the actuator member.
While some of these prior art arrangements have resulted in a simplification for making electrical contact with the electrical circuitry on the printed circuit board, the prior art type connectors to date have not been capable of providing selective engagement of the contact members with the electrical circuitry on the printed circuit board. Rather, with the prior art devices, all of the contact members (at least on one side of the printed circuit board) must either be in the engaged, contact position, or in the non-engaged, non-contact position. This is disadvantageous in that such prior art arrangements do not allow for testing of any individual circuits on the printed circuit board, such as for example to determine malfunctioning or defective components in the electrical circuitry, while the printed circuit board is in the connector. Furthermore, prior art devices do not have the capability of providing different combinations of opened and closed contact members to provide a programmable printed circuit board connector.